A passport photo is a physical object with a size in millimetres, and almost everything that goes wrong at this stage happens inside the print dialog rather than in the image.
Print at 100% scale. Turn off “fit to page”.
Those options shrink the sheet by three to five percent so it clears the printer’s unprintable margin. A 45 mm photo becomes about 43.2 mm, and a head that was at 32 mm becomes 30.2 mm — still inside the range here, but not if you were near an edge of it, and the outer dimensions are wrong regardless.
Why 6 × 4 inches rather than A4
Because 6 × 4 is the one paper size every photo printer, every home printer with a photo tray and every high-street counter handles at a fixed physical size without asking questions. Hand a machine a 6 × 4 file and it prints 6 × 4 inches of paper; hand it an A4 document and it starts negotiating with margins.
It is also the cheapest thing to print. A photo counter charges pennies for a 6 × 4 and treats it as an ordinary holiday snap, whereas asking for “passport photos” at the same counter costs several pounds for the identical piece of paper, because you are paying for someone to operate a booth.
The arithmetic, so you can check it
The sheet is generated at 300 dots per inch, which is 1800 × 1200 pixels for a 6 × 4 inch sheet. One millimetre is 300 ÷ 25.4 ≈ 11.81 pixels, so a UK photo of 35 × 45 mm occupies 413 × 531 pixels on it. 3 fit across and 2 down, with a 2 mm gap between them and a 4 mm margin at the edges, and the grid is centred so the trimming allowance is even all the way round.
None of those numbers is typed into this page. They are computed by the same function that lays out the sheet, so the page cannot describe a layout the tool does not produce — the failure where documentation and behaviour drift apart without anybody noticing.
Paper, and why plain paper fails visibly
The requirement is plain white photographic paper, printed to a professional standard, with no border and no creases or tears. That rules out office paper, and not on a technicality: uncoated paper absorbs ink and lets it spread along the fibres, so edges soften and blacks come out as dark grey. It is obvious at arm’s length, and it is one of the easier reasons for a photograph to be sent back.
Glossy and satin photo paper both work. Matte is acceptable and slightly more forgiving of fingerprints, which matters more than it sounds when the photo has to be handled, signed on the back and posted.
Cutting
The corner marks are deliberately faint and sit outside the photo area, so nothing is printed inside the image that you then have to cut away exactly. With a 2 mm gap there is a millimetre of tolerance either side of the cut, which a craft knife against a steel rule gives you and scissors do not.
Cut all the way through in one pass rather than sawing — a torn edge and a wavy edge are both objectionable for the same reason a crease is. If you are printing at a counter, ask them not to trim: their automatic cutter is set for the paper size, not for your layout.
Frequently asked questions
How do I print a passport photo at the correct size?
Print a 6 × 4 inch sheet at 100% scale on photo paper. The sheet is laid out at 300 DPI, so each photo lands at exactly 35 × 45 mm on paper. The one setting that matters is the scale: "fit to page", "scale to fit" and "shrink oversized pages" all resize the sheet by a few percent, which puts the head outside the permitted range.
How many passport photos fit on a 6 × 4 sheet?
6 at UK size, in a 3 × 2 grid with a 2 mm gap and a 4 mm margin. At US size, which is larger and square, 2 fit in a 2 × 1 grid. Two identical prints are what a UK postal application asks for, so a single sheet covers it several times over.
Can I print them at home?
Yes, on photo paper, with the printer set to its photo or best quality setting and scaling off. Plain office paper will not do: the requirement is plain white photographic paper, and the difference is visible immediately — inkjet ink spreads on uncoated paper and the result looks soft and slightly grey.
Can a high-street photo counter print the sheet?
Yes, and it is usually the better option. Order it as a standard 6 × 4 print — the same size everybody prints holiday photos at — and ask for no cropping or auto-enhance. Their machines print borderless at a fixed physical size, so the scaling problem does not arise. It typically costs less than a pound.
Why 300 DPI?
Because at 300 dots per inch a 35 mm photo is 413 pixels wide, which is comfortably above the 600-pixel digital minimum and at the limit of what the eye resolves at reading distance. Higher makes the file larger without making the print better; lower starts to show.
How do I cut them out?
The sheet carries faint corner marks rather than full lines, so no rule is printed inside the photo area. Cut with a craft knife against a steel rule rather than scissors — a 2 mm gap between photos is not much room to wander, and a wavy edge on the print is itself something the guidance objects to.
Do I still need a digital file?
Only if you apply online, which most people now do — in that case you upload the digital file and never print anything. Prints are for postal applications, and for the other things a passport-style photo gets used for: travel visas, student cards, bus passes, gym memberships and driving licence applications in some countries.